This invention relates to a component for a motor vehicle air brake system, and particularly, to an air supply system which provides enhanced air dryer capacity.
Many motor vehicles and in particular heavy duty trucks incorporate air brake systems which use air pressure to control application of the vehicle service brakes. These systems have an air compressor driven by the vehicle engine which charges a brake system reservoir with high pressure air. The air compressor is controlled to supply air intermittently as needed to replenish the reservoir and maintain reservoir pressure within a predetermined range.
The process of compression of air results in the precipitation of water. Water and particulates in the air brake system can lead to component deterioration and interfere with optimal operation of the brake system. Accordingly, there are various devices used for removing water from the compressed air in air brake systems, known as air dryers. The function of an air dryer is to collect and remove air system contaminants in solid, liquid and vapor form before they enter the brake system. The air dryer provides clean, dry air for the components of the brake system which increases the life of the system and reduces maintenance costs. One type of air dryer incorporates a desiccant material which eliminates daily manual draining of water collection reservoirs as is required in other types of air dryers.
Desiccant type air dryers employ a volume of desiccant material which is hydrophilic and thus absorbs water which passes through an air line from the air compressor. High pressure air enters the desiccant air dryer and the water is stripped by the desiccant material. The air dryer also includes a particulate filter for trapping particulates and oil. Eventually, the desiccant material absorbs water to its maximum capacity. As a means of expelling this trapped water, modern desiccant type air dryers incorporate a backflow or purge air flow as a means of stripping the desiccant of absorbed water. A reservoir referred to as a purge volume is provided with is charged with the high pressure air supplied by the compressor. When the compressor cycles from a loaded mode producing compressed air to the unloaded mode, the purge volume air is allowed to leak to atmosphere through the desiccant bed in a reverse flow direction, stripping it of moisture and expelling it into the air. External purge volume air dryer types use a purge volume reservoir separate from the air dryer and connected to it by an air line. Another type is a so-called integral purge volume type in which the housing which contains a desiccant material also defines the purge volume. These types are in widespread use today and provide excellent performance.
The purging capacity of an air dryer is a significant characteristic which refers to the efficiency with which water trapped by the desiccant is removed during the purge cycle. This purge efficiency is a function of the size of the purge volume. One approach toward increasing purge capacity is to enlarge the purge volume. In the case of either an air dryer with an integral purge volume or a separate purge volume reservoir such requirement results in a larger component being mounted to the vehicle. Enlargement of these components is not always feasible in view of packaging constraints. This is especially true in the case of air dryers having an integral purge volume since there are additional constraints on where they can be mounted.
In view of the foregoing, an object of this invention is to provide an air supply system incorporating an air dryer having a purge volume with enhanced purge capacity without requiring an increase in the overall size of the device.